In recent years, flat panel displays have been utilized in various products and various fields, and there has been demand for a larger size, higher image quality, and lower power consumption in such flat panel displays.
Under such circumstances, organic EL display devices including an organic EL (electroluminescence) element using the electro luminescence of an organic material have been garnering great attention as all-solid flat panel displays capable of being driven at a low voltage and having good high-speed responsiveness, good self-emission characteristics, and the like.
For example, in an organic EL display device of the active matrix type, a thin film-like organic EL element is provided on a substrate on which TFTs (thin film transistors) are provided. In the organic EL element, an organic EL layer including an emissive layer is stacked between a pair of electrodes. The TFTs are connected to one of the pair of electrodes. Then, a voltage is applied between the pair of electrodes to cause the emissive layer to emit light, whereby an image is displayed.
For the above-described conventional organic EL display device, it has been proposed to provide the organic EL element with a sealing film having a sealing membrane in order to prevent the organic EL element from being degraded by moisture and oxygen.
As with the case of the liquid crystal display device, a higher definition has been demanded for the above-described conventional organic EL display device. However, if such a demand for higher definition is to be met, the distance (pitch) between two adjacent sub-pixels is reduced. Accordingly, for the conventional organic EL display device, an edge cover and the like provided between sub-pixels need to be formed with lines and spaces that are very narrow. Further, to achieve such narrow lines and spaces, i.e., high resolution, it is necessary, for example, to minimize the fluidization caused by reflowing during heat curing of an edge cover (vapor-deposited membrane), and to form end portions of the edge cover in a steep pattern. As a result, in the conventional organic EL display device, for example, the oblique sides at end portions of the edge cover have a steep shape.
In the conventional organic EL display device, the reduction of the distance between adjacent two sub-pixels may cause a phenomenon in which a current is leaked in the layer direction of the organic EL layer deposited over the entire pixel, resulting in color mixture. That is, for example, a hole that has entered the organic EL layer from the first electrode at a given sub-pixel travels through the organic EL layer in the layer direction thereof and enters the organic EL layer at the adjacent sub-pixel, thus contributing to light emission in that sub-pixel. Therefore, to solve the problem of color mixture, there have been attempts to increase the thickness of the edge cover so as to increase the effective distance to reach the adjacent sub-pixel, or to make oblique sides of the edge cover steep so as to reduce the thickness of the organic EL layer on the oblique sides, thus increasing the electrical resistance in the layer direction.
As described above, with the conventional organic EL display device, for example, the oblique sides of end portions of the edge cover are formed to have a steep shape or the thickness of the edge cover is increased in order to increase the definition. Consequently, highly dense and sharply defined protruding portions (uneven portions) are formed on the substrate, as a result of which the sealing membrane of the sealing film tends to undergo peeling.
Therefore, for the above-described conventional organic EL display device, it has been proposed to provide a planarization layer included in the conventional sealing film on a substrate, thereby reducing a level difference created by the protruding portions on the substrate, as described in, for example, Patent Document 1 below. With the conventional organic EL display device, a gas barrier layer that completely covers the planarization layer is included in the sealing film to enable preventing moisture and a gas such as oxygen from flowing into the planarization layer.